Smoke Test before using a Flue Gas Analyser

Before commissioning or servicing an oil-fired heating appliance, it is important to perform a smoke test by taking a sample of the flue gases from the boiler flue before using an electronic flue gas analyser. Failing to carry out such a test may result in temporary or permanent damage to the flue gas analyser’s internal components including the oxygen and carbon monoxide sensors.

A smoke test can be accomplished using a smoke test pump and filter paper. To prevent condensation of the flue gases, first warm the smoke test pump body. To obtain a sample of flue gas, insert a clean piece of filter paper into the smoke test pump slot and tighten the clamp.

Take a Sample of the Flue Gases

After the heating appliance has been operating for approximately ten minutes, place the sampling tube of the pump into the test point on the heating appliance flue whilst been careful not to make contact with the internal surfaces of it. This could cause carbon deposits (soot) to enter the sampling tube and produce a smoke spot that provides an incorrect reading.

Check the Smoke Count

Pump the smoke test pump evenly ten times to obtain a sample of the flue gases through the filter paper. Remove the filter paper and compare the smoke spot produced on the filter paper with the smoke count chart provided with the pump. Adjust the burner’s air damper so a smoke count of no more than two is obtained and repeat the test until the desired result is achieved.

Water Vapour Present

If the air damper on the burner is opened excessively then this may produce a wet spot on the filter paper. This wet spot is caused by water vapour within the flue gases that is caused by too much excess air. Simply reduce the amount of air and re-test until there is only a trace or a smoke count of one is achieved.

Consult Manufacturer’s Data

If in the event that the smoke count will not reduce then, if possible, observe the burner flame for instability, misshape or impingement. Recheck the burner’s oil pump pressure against the burner manufacturer’s data and if necessary, replace the burner nozzle with a new burner nozzle to the correct spray angle, flame pattern and output as indicated by the burner manufacturer.

After a satisfactory smoke test, a flue gas analyser can now be used to complete the combustion efficiency testing of the heating appliance.

Electronic Smoke Test Pump

The manual measurement of a smoke count using a smoke test pump, as described above, can be complicated and time consuming. However, with the introduction of the electronic Testo 308, this process has become faster whilst not compromising the accuracy of a smoke test. This instrument will definitely compliment the range of tools, including the flue gas analyser, used by a heating professional in the oil-fired heating appliance industry.